The invention relates to a process for applying a microsystem or transducer to a substrate and to a device which can be produced according to this process in accordance with the preambles of the independent claims.
In the present specification the terms xe2x80x9csensorxe2x80x9d, xe2x80x9cactuatorxe2x80x9d, xe2x80x9ctransducerxe2x80x9d and xe2x80x9cmicrosystemxe2x80x9d are, for reasons of simplicity, grouped under the term xe2x80x9csystemxe2x80x9d. In the case of many such systems, e.g. in many sensors and actuators, apart from the electrical contacting or bonding, there must be further connections to the environment. Part of the system, e.g. a sensitive surface of a humidity sensor, must consequently be open for external influences, e.g. for the external air to be measured. In other words, there must be a connection between a specific part of the system and the environment, so that said part of the system can interact with the environment. However, at the same time other parts of the system must have a good protection against external influences, e.g. moisture, contaminants, corrosive vapours, etc. Such parts requiring protection are e.g. electrical contacts, electronic functional units, circuits or other sensors, which require no opening, e.g. temperature sensors. Therefore the system must be locally selectively packed.
The following are examples of known production processes for locally selectively packed systems:
Dosing method: With a robot-controlled dispenser a wrapping or enveloping material having the correct viscosity is applied to the system in such a way that the desired surface remains free.
Air flow method: Once again a viscous wrapping or enveloping material is applied to the system. In order to obtain a partial surface free from wrapping material, inert gas is blown through a nozzle onto the sensitive surface in such a way that the flow movement of the wrapping material is stopped over said partial surface.
Capillary method: The system to be packed is covered by a cover sheet, which is kept at a small distance from the surface. The viscous wrapping material is drawn between the cover sheet and the system by capillary forces. An opening is made in the cover sheet above the partial surface to be kept open, so that there the wrapping material flow is stopped due to the lack of capillary force and an opening is obtained in the wrapping material.
UV light method: Use is made of a UV-curing sealing compound. In order to keep open a specific partial surface of the system, said partial surface is intensely irradiated with UV light. On application the sealing compound flows over the unilluminated partial surface of the system, solidifying on the edge of the illuminated partial surface, which consequently remains free.
Public method: A punch is pressed onto the partial surface of the system to be kept open, whereas the remaining surface of the system is sealed with viscous wrapping material.
Injection moulding method: Prefabricated injection moulded casings are used for selectively packing the systems.
For the electrical contacting or bonding of the system use is generally made of the wire bonding method, which is well known in microelectronics. In the known production processes for locally selectively packed systems use is consequently made of different processes for the electrical contacting and for the local, selective packing, which do not assist one another. This leads to long production times, higher equipment purchase prices, greater labour and personnel expenditure and ultimately higher product costs. The costs for the housing of such partly open systems can then represent a significant proportion of the total production costs.
A problem of the present invention is to provide a simple, reliable and cost-effective process for the application of a system to a substrate ensuring that at least one partial surface of the system is accessible for external influences and at least one other partial surface is protected against external influences. A further problem of the invention is to provide a device which can be produced in simple, inexpensive manner using said process.
The problem is solved by the process and device according to the invention, as defined in the independent claims.
A system, which is to be applied to a substrate, has at least one first partial surface, whose interaction with the environment is to be possible after performing the process, and at least one second partial surface, which is to be protected against external influences. In the process according to the invention, initially the substrate is prepared, at least one passage point suitable for the intended interaction being produced in the substrate. Such a passage point is preferably constructed as at least one opening in the substrate. The system and the substrate are so mutually positioned, that the at least one first partial surface faces the substrate and that the at least one passage point in the substrate and the at least one first partial surface come to rest facing one another. Contacts are produced at contact points provided, preferably with one of the known flip-chip technologies. The contacts link the system and the substrate mechanically and/or electrically, i.e. at least one contact can be electrically conductive. Outside the contacts the system and substrate normally have a spacing from one another such that at least one space or gap is formed.
The above-described basic form of the production process according to the invention already ensures local selective packing, i.e. the protection of the at least one second partial surface. The at least one second partial surface is e.g. protected against contact with external objects, liquid splashes from the outside, etc. However, for many applications a hermetic seal is required. According to the invention, a hermetic seal can be ensured using one of the three following variants.
In a first variant at least one contact is produced, which completely surrounds the at least one passage point in the substrate. Thus, such a sealing contact seals the at least one second partial surface in hermetic manner against external influences. The greatest advantage of this variant is that the same process is used for producing both the electrical contacting and for the local, selective packing, so that production is particularly simple, reliable and inexpensive.
In a second variant the gap between the system and the substrate is at least partly filled with an initially liquid or viscous filling material, whilst making use of capillary forces. In the vicinity of the at least one passage point in the substrate the capillary forces are too small or are completely missing, so that the filling material does not wet the at least one first partial surface. The filling material is subsequently cured and hermetically seals the at least one second partial surface against external influences, whereas the at least one first partial surface is open. The advantages of this variant are that the sealing is in certain circumstances more effective, because it is in full-surface form. The filling material simultaneously ensures an even better cohesion between system and substrate. In addition, the filling material compensates varying thermal expansions of the system and the substrate.
A third variant is constituted by the combination of the first and second variants. Thus, a sealing contact is produced around the at least one first partial surface and the at least one second partial surface is at least partly sealed with a sealing filling material. In this third variant the sealing contact need not necessarily completely surround the at least one passage point, but the at least one second partial surface is still hermetically sealed. An advantage of this variant is that the sealing contact serves as a barrier for the filling material, so as to define an exact boundary between the sealed and the unsealed area. The third variant also combines most of the advantages of the first two variants.
The device according to the invention producible by the aforementioned process can e.g. be used for flow sensors, viscosity sensors, moisture sensors, force sensors, pressure sensors, sensors for electromagnetic radiation, sensors for particle radiation or chemical sensors.